[JJ’s] Tesla coil is a uses two microwave oven transformers as a power supply. He also uses an Asynchronous Rotary Spark Gap (ASRG). As the name implies, a rotary spark gap uses a motor to turn a rotor. At certain points in the rotation, the rotor creates a small enough gap that a high voltage spark can jump across, energizing the primary coil. This idea is similar to an automotive ignition system distributor. [Pete] gives a great example of an ASRG in this video. Most ASRG based Tesla coils use the small motor to spin up the spark gap. Varying the speed of the motor creates the characteristic “motor revving” noise heard in the final arcs of the Tesla Coil.

[JJ] made things a bit more interesting by installing a couple of fluorescent bulbs inside a pumpkin near the coil. The coil lights them easily, and they glow even brighter when the pumpkin is struck. Still not satisfied, he also donned his grounded chainmail gloves and drew the arc to himself. We always love seeing people safely taking hits from massive Tesla coils, but this definitely falls under the “don’t try this at home” banner.

Throughout the maker pavilion, the siren song of a musical Tesla coil could be heard. Those who followed their ears found themselves at the oneTesla booth. OneTesla is a hobby Tesla coil, with the added twist of polyphonic MIDI input.

Started by three MIT students, oneTesla had a successful Kickstarter campaign last year. Like many kickstarters, they are a bit behind in the shipping department. They are shipping out their third run of kits to backers now. The group had a small number of oneTesla coils for sale at the show, which appeared to have sold out by midday Sunday.

The actual process of generating sound with a Tesla coil is fascinating. All Tesla coils are resonant at high frequency. In oneTesla’s case, this is 220kHz. Human hearing ends around 20kHz, so this is well beyond the range of perception. Since the coil is locked in at this frequency, the power to the coil is modulated at the desired sound frequency. Playing an A note for example, would mean modulating the coil at 440Hz.

A few years ago [Patrick] was offered the Tesla coil of a friend of a friend. This was an opportunity too good for him to pass up.

He then began the creation of an Off-Line Tesla Coil (OLTC), where no supply transformer is used. The incoming mains supply is rectified and directly fed into the tank capacitor.

[Patrick] therefore had to build a huge capacitor bank and more importantly his own primary coil, made with a 1.6mm (0.064″) copper sheet to handle the immense current involved. Air cooling the electronics was sufficient until he started using his three phase input supply. As more power involves more heat, a waterblock was designed to cool the main transistor.

Patrick’s write-up is very detailed and worth the read. Once you’re finished with it, we advise you to browse through his website, where a lot more cool projects are described.

Last week we caught wind of a piece from the Today Show that shows very technically minded thieves stealing cars with a small device. Cops don’t know how they’re doing it, and of course the Today show (and the Hackaday comments) were full of speculation. The top three theories for how these thieves are unlocking car doors are jamming a keyless entry’s ‘lock signal’, a radio transmitter to send an ‘unlock’ code, or a small EMP device touched to the passenger side door to make it unlock.

That last theory – using a small EMP device to unlock a car’s door – got the attention of someone who builds mini EMP devices and has used them to get credits on slot machines. He emailed us under a condition of anonymity, but he says it’s highly unlikely a mini EMP device would be able to activate the solenoid on a car door.

This anonymous electromagnetic wizard would like to open up a challenge to Hackaday readers, though: demonstrate a miniature EMP device able to unlock an unmodified car door, and you’ll earn the respect of high voltage tinkerers the world over. If you’re successful you could always sell your device to a few criminal interests, but let’s keep things above board here.

[Thor’s] hammer, Mjolnir, is pretty freaking awesome. It can only be picked up by [Thor], he can use it to fly, and probably the coolest part, it can summon lightning. After watching the first movie, and goofing around with the guys at ArcAttack, I had this idea that I could stuff a tiny tesla coil into a mjolnir and end up with a really cool prop.

At this point, I had to make a decision. I was either going to go portable and live with small arcs, or make this a stationary piece and hide a giant tesla coil in a base. It would have bigger arcs, but I couldn’t carry it around. While I may re-visit the stationary version at some point, I ultimately decided I wanted to be able to wander around and play with this thing.

I had seen some videos of [Staci Elaan] showing off her battery-powered coils and I really liked her results. I figured, with her experience, she could probably do a better job than I could on getting the most bang out of a small package. She was happy to be involved and delivered a small 12v powered coil for me to work with. I should also point out that the coils [Staci] makes are usually donated to educational groups. This woman is awesome.

Playstation π

Yeah, it’s another home made Raspberry Pi case, but [Gabriel]’s Mini Playstation 3.14 is the bee’s knees. The enclosure was once a metal gift box originally intended for gift cards. With a few whacks of a Dremel, the world finally has a new PS3 that runs Linux.

Up there with The Secret Life of Machines

[Mattias] sent in a tip about a really cool TV show airing in Sweden. It’s called Mekatronik, and it’s basically the interesting parts of Mythbusters where [Jamie] and [Adam] build random cool stuff. It’s a Swedish language program, so if anyone would like to make some subs for the episodes, we’ll be more than happy to link to it again.

Web-based software defined radio

The amateur radio club at University of Twente in the Netherlands came up with something really cool: a web-based software defined radio. So what, you ask? It’s just streaming audio or something over the Internet? Nope. You can actually control this SDR over the web.

We’re deeply sorry for turning the hardware turn to slag. Really, we are.

Junk box Tesla coil

[JJ] whipped up a homemade Tesla coil out of junk he had lying around. Basically, it’s a piece of PVC pipe, a tennis ball, and aluminum foil. Even the transformer was pulled from a long-forgotten project. [JJ] is getting some really good arcs, so we’ll call this a win.

Time circuits active

[Danilo] was invited to a costume party with a movie theme. He wanted something Back to the Future-is, so he whipped up a flux capacitor (translation). It’s based on a PIC12F675, with the microcontroller running a bit of code that flashes the LEDs just like the movie. Now on to the hoverboard project…

It’s a bit difficult to estimate the size of the Tesla coil from this picture, but look closely at the hand rail on the red-orange wall to the left and that helps. The 10-foot tall musical Tesla Coil project has been on-going for about two years. But the team at X-Labs — a hackerspace affiliated with the University of South Florida — finished it just in time for the University’s engineering expo later in the month. There’s some information about it to be found in the recent student newspaper article on the project. A lot more build details are found on the groups website, although that post is quite old.

You can’t call it a musical coil unless there’s a demo video, and that can be seen after the jump. What better to test the thing than by playing the Super Mario Bros. theme? We’re actually more partial to the Imperial March (it’s also fun to hear played on stepper motors).